The present invention relates to the field of foundry operations and more particularly to the casting of molten metal in a production line environment. In greater particularity the present invention relates to a technique for casting molten metal in a production process utilizing a conveyable string of molds that define a series of mold cavities. In still further particularity, the present invention relates to an apparatus and method for preventing the premature introduction of molten metal into a mold cavity formed by a conveyable string of molds as the mold string is advanced stepwise along a conveying system in a metal casting process.
The art of casting metal objects in sand molds is ancient. Numerous advances have been made in the art, and metal casting may now be accomplished by complex, automated production techniques utilizing a conveyable string of closely juxtaposed molds that are advanced along a production line. A mold string used in well known production casting systems typically comprises multiple adjacent molds, each distinct mold defining a mold cavity and at least one passageway, referred to as a downsprue, leading from the mold cavity to a surface of the mold. In the production method, castings are formed by introducing molten metal into the downsprue of a mold to fill the mold cavity and thereafter allowing the molten metal to cool to form a solid casting. Economic constraints require increasing efficiency in the casting process, and it is well known in the art that it is desirable that individual castings be formed in relatively short time intervals without having an adverse impact on the quality of the metal casting.
Metal casting production techniques utilizing a conveyable mold string require a source of molten metal and a method of transferring selective quantities of molten metal from a molten metal source to individual molds. In the production line casting of molten metal, molten metal is typically provided in batches stored in a large reservoir or ladle. An efficient and commonly used method of transferring molten metal into individual molds from the source of molten metal is to pour molten metal from a source into the downsprue of a mold. Utilization of this method of transferring requires positioning the source of molten metal, such as a reservoir or ladle, above the mold string.
A common method of pouring molten metal from a molten metal reservoir is to selectively open and close an outlet located in the bottom portion of a molten metal reservoir, such as with the use of a stopper rod positioned within the reservoir that can be raised to open the outlet and lowered to close the outlet. This method of transferring molten metal into individual molds often involves aligning the downsprue of an individual mold directly below the effluent outlet of a molten metal reservoir for the receipt of the molten metal poured from the reservoir outlet.
Production methods of the type utilizing a source of molten metal disposed directly above a conveyable mold string typically utilize a specific type of mold string having downsprues extending from the top surface of the mold string. In the casting process, the mold string of this type is indexed to position a first individual mold beneath the molten metal source so that the downsprue in the top surface of the mold string is aligned directly below the outlet. In a typical production casting process, the mold string remains in a stationary position as the outlet is opened to fill the mold with molten metal. After the selected amount of molten metal has been poured into the mold, the outlet is closed to cease the transfer of molten metal. The mold string is then indexed, or advanced, along a conveying system to a next stationary position in which a next mold being adjacent to the first individual mold is aligned directly beneath the outlet of the molten metal source. This next mold is then filled with molten metal and this process is repeated in sequence to progressively fill adjacent molds with molten metal.
Various techniques for producing a mold string defining a series of mold cavities and downsprues extending from the top surface of the mold string are commercially available and widely utilized. A mold string of this general type may be manufactured in connection with metal casting in vertically-parted green sand molds, and in connection with molds produced utilizing the well known Disamatic machine. Other similar methods of such production of mold strings are well known in the art.
Without regard to the specific manner in which a particular mold string is produced, mold strings typically utilized in production line casting techniques comprise a series of vertically parted molds wherein each mold defines a mold cavity and a downsprue extending from the top surface of the mold string. There is a continual problem relating to the use of vertically parted molds such as those produced by a Disamatic molding machine and other common production techniques. Such molds are in relatively close proximity to adjacent molds, and in actual operation molten metal intended for introduction into specific mold cavities may instead be ultimately deposited on the top surface of a mold string. This can result in the unintended and premature introduction of molten metal into an empty mold cavity, which causes serious defects in the resulting quality of produced castings. Molten metal prematurely introduced into an empty mold cavity cools to form small droplets of metal commonly referred to as xe2x80x9cshots.xe2x80x9d The casting process is typically not designed for the random and unintended introduction of shots into an empty mold cavity prior to filling the mold cavity with molten metal. Instead, the casting process is designed to fill mold cavities that are entirely empty. This allows the molten metal introduced into the mold cavity to have substantially uniform metallurgical properties.
The premature introduction of shots into an empty mold cavity can result in the production of castings having significant defects. The shot produces an inclusion in the casting causing scrap or, worse, resulting in the failure of a safety part. The molten metal poured into the mold may not adhere properly to the shot or the shot may otherwise adversely influence the cooling properties of the molten metal proximate the shot. The premature introduction of even small droplets of molten metal forming shot into an empty mold cavity results in serious defects in the quality of produced castings. Therefore, methods of preventing the premature introduction of shot into molds in a casting process is needed.
One manner in which this quality control problem initially occurs is by the splashing of molten metal from one mold to an adjacent mold during pouring of molten metal. Methods of preventing this type of manufacturing problem are disclosed in the prior art. Sorrell et al., U.S. Pat. No. 4,749,019 discloses the utilization of a splash guard in a metal casting process for preventing molten metal from splashing into the downsprue of a mold as molten metal is poured into an adjacent mold cavity. The Sorrell et al. device is a solid object that is selectively placed between adjacent molds during the pouring of molten metal. In a manual casting process, a portion of the Sorrell et al. device physically contacts a portion of the top surface of the mold string and remains in this position as molten metal is poured. After molten metal has been poured into a cavity, the splash guard disclosed in the Sorrell et al. patent is then raised from the top surface of the mold string. The Sorrell et al. device remains in a raised position as the mold string is indexed to the next position.
A second embodiment of the device disclosed in the Sorrell et al. patent is directed for use in an automated production process. In the second embodiment, the splash guard remains in a fixed raised position above the top surface of the mold string. These and other conventional methods of preventing the premature introduction of molten metal into an empty mold cavity address the problem of the spillage of molten metal between adjacent molds during pouring of molten metal.
A significant limitation in the conventional methods of preventing the introduction of shot into an empty mold is that these methods do not address the continual problem of the spillage of molten iron between adjacent molds occurring as a result of the movement of the mold string during the production process. For example, the previously discussed Sorrell et al. device is placed in a raised position off the surface of a mold string as the mold string is indexed. Thus, the Sorrell et al. device does not prevent the introduction of molten metal into a downsprue when the mold string is in motion.
The metal casting process industry is highly competitive, and to address competitive pressures it is generally desirable to improve the efficiency of the production process. A readily apparent method to do so is increasing the speed at which the mold string is advanced during the production process, so that individual castings may be formed in a relatively short time frame. Increasing the indexing speed requires reducing the period of time that a mold string is moved from an initial stationary position to a second stationary position. By necessity, it can be appreciated that increasing the overall indexing speed requires a higher rate of acceleration from which a mold string is moved from an initial stationary position. Thus, generally, as metal casting processes become increasingly more efficient, mold strings are generally indexed at increasingly higher speeds.
The problem not addressed in conventional methods of casting results from the presence of molten metal on the top surface of a mold cavity as the mold string is advanced in a casting production process. As is well known in the art, a mold string for use in a casting process commonly defines a substantially continuous top surface between adjacent downsprues. Although unintended, during the operation of a production casting method, molten metal may be spilled, splashed, or overflowed onto the top surface of the mold string during the pouring or indexing steps. The acceleration of a mold string from a stationary position causes, which can be abrupt, causes movement of spilled molten metal across the substantially continuous top surface of the mold string, often resulting in the premature introduction of molten metal into an empty mold cavity.
Whether caused by the splashing of molten metal during the pouring process or by the movement of the mold string, quality control problems resulting from the premature introduction of molten metal into an empty mold cavity in a casting process are equally serious. To address the limitations of the prior art and to improve the quality and efficiency of metal castings, what is needed is an apparatus and method for preventing the premature introduction of molten metal into a mold cavity formed by a conveyable string of molds as the mold string is advanced stepwise along a conveying system in a metal casting process.
It is an object of the present invention to provide an improved method of casting metal.
An additional object of the present invention is to provide an apparatus and method for improving the quality of metal castings produced in the production line casting of molten metal.
A further object of the present invention is to prevent defects in castings produced in the production line casting of molten metal resulting from the spillage of molten metal between adjacent molds in a conveyable string of closely juxtaposed molds.
An additional object of the present invention is to provide an apparatus and method for preventing the inadvertent and premature introduction of molten metal into a mold cavity formed by a conveyable string of molds as the mold string is indexed in a metal casting process.
A still further object of the present invention is to provide an apparatus and method for preventing the premature introduction of molten metal into a mold cavity that may be adapted for use in casting processes that are both manually and automatically operated.
These and other objects of the invention are provided by a mold riding shot blocker designed for use with prior well known production casting systems utilizing conveyable mold strings comprising closely juxtaposed molds that define a substantially continuous top surface, a series of mold cavities, and a series of downsprues extending from said mold cavities to the top surface. The mold riding shot blocker of the present invention comprises a solid object having a configuration suitable for placement on the top surface of a mold string so that when the solid object is placed on the top surface of a mold string, at least one downsprue extending from the top surface of the mold string is covered. Being at rest on the top surface of the mold string, the solid object provides a barrier that prevents the premature introduction of molten iron into any downsprue covered by the solid object. Although the preferred embodiment discloses a solid object being a blocking bar having a rectangular configuration and a substantially flat top and bottom surfaces, solid objects having other configurations suitable for placement on a mold string to cover at least one downsprue are contemplated. The invention further comprises a means for lowering the solid object onto the top surface of a mold string and raising the solid object off the top surface of a mold string to cover and uncover at least one downsprue during movement of the mold string along a conveying system in a metal casting process.
The present invention further comprises a method for blocking the spillage of molten metal between adjacent molds in a conveyable string of closely juxtaposed molds as the mold string is advanced in a stepwise cycle in a metal casting process. The method is directed for use with a mold string comprised of molds that define a top mold surface, a casting cavity, and at least one mold inlet extending from the casting cavity to the top mold surface. The method comprises the steps of positioning a solid object having a configuration suitable for placement on the top surface of a mold string, lowering the solid object into protective position on a top surface of a first mold with the mold string in a stationary first position to cover at least one mold inlet of the first mold. The method of the present invention further comprises the step of indexing the conveyable mold string with the blocking bar riding on the mold string in a protective position during at least a portion of a stepwise cycle comprising the movement of the conveyable mold string from a stationary first position to a stationary second position. The method also comprises the step of raising the solid object away from the top surface of the first mold to uncover at least one mold inlet.
The apparatus and method of the present invention thus overcomes the limitations of the prior art by preventing the inadvertent premature introduction of molten metal, or shot, into an empty mold cavity of a mold string as the mold string is advanced stepwise in a casting production process. The mold riding shot blocker is placed on the top surface of mold string to cover at least one downsprue. With a downsprue covered, an adjacent mold is filled with molten metal. Upon completion of filling an adjacent mold with molten metal, the mold string may be indexed with the mold riding shot blocker remaining in a protective position on the mold string. During the period of time the mold riding shot blocker remains in a protective position atop the mold string, the mold riding shot blocker provides a barrier for introduction of molten metal into the covered downsprue. Thus the present invention overcomes the limitations of the prior art by providing a barrier for the covered downsprue not only during the filling of an adjacent mold with molten metal but also during indexing of the mold string along the production process.
Although the present invention may be manually operated, the present invention further comprises a control means such as a micro-processor for automating the process of selectively raising and lowering the mold riding shot blocker to coordinate the operation of the invention with a highly automated casting production process. Specifically, the raising and lowering of the present invention can be automatically coordinated with the indexing of the mold string and the pouring of molten metal into successive mold cavities.